1. Field of the Invention
This invention relates to an image processing apparatus switchable between an observation mode in which an image of an original, such as a microfilm or the like, is projected onto a screen to observe the image, and a read mode in which the image is projected onto an image sensor to convert it into an electrical image signal.
2. Description of the Prior Art
A conventional image reading apparatus is shown in FIG. 6. An image of a microfilm F is magnified, reflected by mirrors 106 and 107, and projected onto a screen 108. On the other hand, when the image is read by an image sensor S, a moving mirror 120 first enters into an image projection optical path, and stops at position 120' (shown by broken lines). The light beam of the image is then reflected by the moving mirror 120' and a mirror 121, and is projected onto line "a". The image sensor S then moves along line "a" in the direction of the arrow up to point S' to read the image of the microfilm F.
In such a conventional apparatus, the image sensor S moves outside the image projection optical path for the screen, and is placed in the reflection optical path of the mirror 121 dedicated for reading, which is placed outside the image projection optical path. Hence, there are problems in that a large space dedicated for reading is needed, the entire apparatus thereby becomes large, the structure of the apparatus becomes complicated, and the apparatus therefore becomes expensive.
There has also been known a method in which an image sensor is movably provided behind the screen, and the image of the film is read by moving the image sensor along the screen. In this method, however, there is the problem in that, since the image sensor is placed at a position off the imaging position of the image on the screen, focus adjustment must be performed every time the image is read by the image sensor, and hence it is necessary to separately perform focus adjustment for the screen and the image sensor.
There is also a problem in that the image sensor is influenced by external light.